421,915 research outputs found
Evaluation of ASTER GDEM ver2 using GPS measurements and SRTM ver4.1 in China
The freely available ASTER GDEM ver2 was released by NASA and METI on October 17, 2011. As one of the most complete high resolution digital topographic data sets of the world to date, the ASTER GDEM covers land surfaces between 83°N and 83°S at a spatial resolution of 1 arc-second and will be a useful product for many applications, such as relief analysis, hydrological studies and radar interferometry. The stated improvements in the second version of ASTER GDEM benefit from finer horizontal resolution, offset adjustment and water body detection in addition to new observed ASTER scenes. This study investigates the absolute vertical accuracy of the ASTER GDEM ver2 at five study sites in China using ground control points (GCPs) from high accuracy GPS benchmarks, and also using a DEM-to-DEM comparison with the Consultative Group for International Agriculture Research Consortium for Spatial Information (CGIAR-CSI) SRTM DEM (Version 4.1). And then, the results are separated into GlobCover land cover classes to derive the spatial pattern of error. It is demonstrated that the RMSE (19m) and mean (-13m) values of ASTER GDEM ver2 against GPS-GCPs in the five study areas is lower than its first version ASTER GDEM ver1 (26m and -21m) as a result of the adjustment of the elevation offsets in the new version. It should be noted that the five study areas in this study are representative in terms of terrain types and land covers in China, and even for most of mid-latitude zones. It is believed that the ASTER GDEM offers a major alternative in accessibility to high quality elevation data
A guided Monte Carlo method for optimization problems
We introduce a new Monte Carlo method by incorporating a guided distribution
function to the conventional Monte Carlo method. In this way, the efficiency of
Monte Carlo methods is drastically improved. To further speed up the algorithm,
we include two more ingredients into the algorithm. First, we freeze the
sub-patterns that have high probability of appearance during the search for
optimal solution, resulting in a reduction of the phase space of the problem.
Second, we perform the simulation at a temperature which is within the optimal
temperature range of the optimization search in our algorithm. We use this
algorithm to search for the optimal path of the traveling salesman problem and
the ground state energy of the spin glass model and demonstrate that its
performance is comparable with more elaborate and heuristic methods.Comment: 4 pages, ReVTe
Riemann-Liouville processes arising from Branching particle systems
It is proved in this paper that Riemann-Liouville processes can arise from
the temporal structures of the scaled occupation time fluctuation limits of the
site-dependent (d,\alpha,\sigma(x))branching particle systems in the case of
1=d<\alpha<2 and \int_{\R}\sigma(x)\d x<\infty.Comment: 12 page
ArticleRank: a PageRank-based alternative to numbers of citations for analysing citation networks
Purpose - The purpose of this paper is to suggest an alternative to the widely used Times Cited criterion for analysing citation networks. The approach involves taking account of the natures of the papers that cite a given paper, so as to differentiate between papers that attract the same number of citations.
Design/methodology/approach - ArticleRank is an algorithm that has been derived from Google's PageRank algorithm to measure the influence of journal articles. ArticleRank is applied to two datasets - a citation network based on an early paper on webometrics, and a self-citation network based on the 19 most cited papers in the Journal of Documentation - using citation data taken from the Web of Knowledge database.
Findings - ArticleRank values provide a different ranking of a set of papers from that provided by the corresponding Times Cited values, and overcomes the inability of the latter to differentiate between papers with the same numbers of citations. The difference in rankings between Times Cited and ArticleRank is greatest for the most heavily cited articles in a dataset.
Originality/value - This is a novel application of the PageRank algorithm
QCD resummation for light-particle jets
We construct an evolution equation for the invariant-mass distribution of
light-quark and gluon jets in the framework of QCD resummation. The solution of
the evolution equation exhibits a behavior consistent with Tevatron CDF data:
the jet distribution vanishes in the small invariant-mass limit, and its peak
moves toward the high invariant-mass region with the jet energy. We also
construct an evolution equation for the energy profile of the light-quark and
gluon jets in the similar framework. The solution shows that the energy
accumulates faster within a light-quark jet cone than within a gluon jet cone.
The jet energy profile convoluted with hard scattering and parton distribution
functions matches well with the Tevatron CDF and the large-hadron-collider
(LHC) CMS data. Moreover, comparison with the CDF and CMS data implies that
jets with large (small) transverse momentum are mainly composed of the
light-quark (gluon) jets. At last, we discuss the application of the above
solutions for the light-particle jets to the identification of highly-boosted
heavy particles produced at LHC.Comment: 22 pages, 13 figure
Ratcheting Heat Flux against a Thermal Bias
Merely rocking the temperature in one heat bath can direct a steady heat flux
from cold to hot against a non-zero thermal bias in stylized nonlinear lattice
junctions that are sandwiched between two heat baths. Likewise, for an average
zero-temperature difference between the two contacts a net, ratchet-like heat
flux emerges. Computer simulations show that this very heat flux can be
controlled and reversed by suitably tailoring the frequency ( 100
MHz) of the alternating temperature field.Comment: 5 pages, 6 figure
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